The X-Frame-Options HTTP response header is a common method to protect against the clickjacking vulnerability since it is easy to implement and configure, and all modern browsers support it. As awareness of clickjacking has grown in the past several years, I have seen more and more Qualys customers adopt X-Frame-Options to improve the security of their web applications.

However, I have also noticed there is a common implementation mistake that causes some web applications to be vulnerable to clickjacking attack even though they have X-Frame-Options configured. In this article, I describe the implementation mistake and show how to check your web applications to ensure X-Frame-Options is implemented correctly.